1. Field of the Invention
The present invention relates to a plasma display device for displaying an image, and a method of driving a plasma display panel.
2. Description of the Related Art
Various types of flat display devices are commercialized. One of them is an AC-type (AC discharge type) plasma display panel. The plasma display panel has two substrates, i.e., a front glass substrate and a rear glass substrate, which are disposed opposite to each other across a predetermined gap. The front glass substrate is a display surface of the plasma display panel. On the inner surface of the front glass substrate (i.e., surface facing the rear glass substrate), a plurality of row electrode pairs, which extend in parallel with each other, are formed as sustain electrode pairs. On the rear glass substrate, a plurality of column electrodes are formed as addressing electrodes which extend perpendicular to the row electrode pairs. A fluorescent material is coated over the rear glass substrate. When viewed from the display surface side, display cells which serve as pixels are formed at intersections of the row electrode pairs with the column electrodes. A multi-grayscale (gradation) driving sequence using a sub-field method is performed for such a plasma display panel in order to generate an expected halftone display luminance faithful to an input video signal.
In the gradation driving sequence based on the sub-field method, one field of video signal is divided into a plurality of sub-fields and each sub-field is assigned a predetermined number of light emission (or a predetermined period of light emission). Display driving is performed for one field using such sub-fields. In each sub-field, an addressing process and a sustain process are executed in sequence. In the addressing process, a discharge is selectively produced between the row electrodes and the column electrode within each display cell in accordance with an input video signal to form (or erase) a predetermined amount of wall charge. This discharge is called selective discharge. In the sustain process, only those display cells which have the wall charge are forced to repeatedly discharge to maintain a light emitting state associated with the discharge. An initialization process is executed prior to the addressing process at least in the first sub-field. In the initialization process, a reset discharge is produced between two electrodes in each row electrode pair of all the display cells to initialize the amount of wall charge remaining in all the display cells.
The reset discharge is a relatively strong discharge, and does not at all contribute to the contents of an image to be displayed, so that the light emission associated with this discharge degrades the contrast of the image.
Another type of plasma display device was proposed to deal with this problem (see FIG. 13 in Japanese Patent Kokai No. 2001-188509). This plasma display device employs T-shaped row electrodes for producing a discharge. A reset pulse whose voltage slowly changes at a rising edge is applied to the T-shaped row electrodes (see FIG. 7 in Japanese Patent Kokai No. 2001-188509) to produce a weak reset discharge. A light emission luminance associated with the reset discharge is reduced because of the weakened reset discharge, so that the contract is enhanced. In order to produce the reset discharges in all display cells with such a reset pulse, the peak voltage of the reset pulse must be relatively high.
However, a high peak voltage value of the reset pulse can cause a strong discharge to be produced not only between the two electrodes in each row electrode pair but also between the row electrode(s) and column electrode. This results in a lower contrast. Also, the strong discharge produced between the row electrode and column electrode creates the wall charge more than the desired amount. This could trigger erroneous selective discharge in the addressing process. As a consequence, the quality of displayed images drops.